<template>
    <canvas
        :ref="domId"
        class="app-sign-canvas" :id="domId"
        @mousedown.prevent.stop="handleMousedown"
        @mousemove.prevent.stop="handleMousemove"
        @mouseup.prevent.stop="handleMouseup"
        @mouseleave.prevent.stop="handleMouseleave"
        @touchstart.prevent.stop="handleTouchstart"
        @touchmove.prevent.stop="handleTouchmove"
        @touchend.prevent.stop="handleTouchend">
        您的浏览器不支持canvas技术,请升级浏览器!
    </canvas>
</template>
<script>
    export default {
        name: 'SignCanvas',
        model: {
            value: 'image',
            event: 'confirm'
        },
        props: {
            image: {
                required: false,
                type: [String],
                default: null
            },

            options: {  //配置项
                required: false,
                type: [Object],
                default: () => null
            },

        },
        data () {
            return {
                value: null, //base64
                domId: `sign-canvas-${Math.random().toString(36).substr(2)}`,  //生成唯一dom标识
                canvas:null,    //canvas dom对象
                context:null,   //canvas 画布对象
                dpr: 1,
                config: {
                    isDpr: false,       //是否使用dpr兼容高分屏 [Boolean] 可选
                    lastWriteSpeed: 1,  //书写速度 [Number] 可选
                    lastWriteWidth: 2,  //下笔的宽度 [Number] 可选
                    lineCap: 'round',   //线条的边缘类型 [butt]平直的边缘 [round]圆形线帽 [square]	正方形线帽
                    lineJoin: 'round',  //线条交汇时边角的类型  [bevel]创建斜角 [round]创建圆角 [miter]创建尖角。
                    canvasWidth: 350, //canvas宽高 [Number] 可选
                    canvasHeight: 300,  //高度  [Number] 可选
                    isShowBorder: true, //是否显示边框 [可选]
                    bgColor: '#fcc', //背景色 [String] 可选 注:这背景色仅仅只是canvas背景,保存的图片仍然是透明的
                    borderWidth: 1, // 网格线宽度  [Number] 可选
                    borderColor: "#ff787f", //网格颜色  [String] 可选
                    writeWidth: 5, //基础轨迹宽度  [Number] 可选
                    maxWriteWidth: 30, // 写字模式最大线宽  [Number] 可选
                    minWriteWidth: 5, // 写字模式最小线宽  [Number] 可选
                    writeColor: '#101010', // 轨迹颜色  [String] 可选
                    isSign: false, //签名模式 [Boolean] 默认为非签名模式,有线框, 当设置为true的时候没有任何线框
                    imgType:'png'   //下载的图片格式  [String] 可选为 jpeg  canvas本是透明背景的
                }
            };
        },
        mounted () {
            this.init();
        },

        watch:{
            options:{
                handler(){
                    this.init();
                },
                deep: true
            }
        },

        methods: {
            init () {
                const options = this.options;
                if (options) {
                    for (const key in options) {
                        this.config[key] = options[key];
                    }
                }
                this.dpr = typeof window !== 'undefined' && this.config.isDpr ? window.devicePixelRatio || window.webkitDevicePixelRatio || window.mozDevicePixelRatio || 1 : 1;
                this.canvas = document.getElementById(this.domId);
                this.context = this.canvas.getContext("2d");
                this.canvas.style.background = this.config.bgColor;
                this.canvas.height = this.config.canvasWidth;
                this.canvas.width = this.config.canvasHeight;
                this.canvasInit();
                this.canvasClear();
            },

            /**
             * 轨迹宽度
             */
            setLineWidth () {
                const nowTime = new Date().getTime();
                const diffTime = nowTime - this.config.lastWriteTime;
                this.config.lastWriteTime = nowTime;
                let returnNum = this.config.minWriteWidth + (this.config.maxWriteWidth - this.config.minWriteWidth) * diffTime / 30;
                if (returnNum < this.config.minWriteWidth) {
                    returnNum = this.config.minWriteWidth;
                } else if (returnNum > this.config.maxWriteWidth) {
                    returnNum = this.config.maxWriteWidth;
                }
                returnNum = returnNum.toFixed(2);
                //写字模式和签名模式
                if (this.config.isSign) {
                    this.context.lineWidth = this.config.writeWidth * this.dpr;
                } else {
                    const lineWidth = this.config.lastWriteWidth = this.config.lastWriteWidth / 4 * 3 + returnNum / 4
                    this.context.lineWidth = lineWidth * this.dpr;
                }
            },

            /**
             * 写开始
             */
            writeBegin (point) {
                this.config.isWrite = true;
                this.config.lastWriteTime = new Date().getTime();
                this.config.lastPoint = point;
                this.writeContextStyle();
            },

            /**
             * 绘制轨迹
             */
            writing (point) {
                this.context.beginPath();
                this.context.moveTo(this.config.lastPoint.x * this.dpr, this.config.lastPoint.y * this.dpr);
                this.context.lineTo(point.x * this.dpr, point.y * this.dpr);
                this.setLineWidth();
                this.context.stroke();
                this.config.lastPoint = point;
                this.context.closePath();
            },

            /**
             * 写结束
             */
            writeEnd (point) {
                this.config.isWrite = false;
                this.config.lastPoint = point;
                this.saveAsImg();
            },

            /**
             * 轨迹样式
             */
            writeContextStyle () {
                this.context.beginPath();
                this.context.strokeStyle = this.config.writeColor;
                this.context.lineCap = this.config.lineCap;
                this.context.lineJoin = this.config.lineJoin;
            },


            /**
             * 清空画板
             */
            canvasClear () {
                this.context.save();
                this.context.strokeStyle = this.config.writeColor;
                this.context.clearRect(0, 0, this.canvas.width, this.canvas.height);
                this.context.beginPath();
                this.context.lineWidth = this.config.borderWidth * this.dpr;
                this.context.strokeStyle = this.config.borderColor;
                let size = this.config.borderWidth / 2 * this.dpr;
                if(this.config.isShowBorder){
                    //画外面的框
                    this.context.moveTo(size, size);
                    this.context.lineTo(this.canvas.width - size, size);
                    this.context.lineTo(this.canvas.width - size, this.canvas.height - size);
                    this.context.lineTo(size, this.canvas.height - size);
                    this.context.closePath();
                    this.context.stroke();
                }
                if (this.config.isShowBorder && !this.config.isSign) {
                    //画里面的框
                    this.context.moveTo(0, 0);
                    this.context.lineTo(this.canvas.width, this.canvas.height);
                    this.context.lineTo(this.canvas.width, this.canvas.height / 2);
                    this.context.lineTo(0, this.canvas.height / 2);
                    this.context.lineTo(0, this.canvas.height);
                    this.context.lineTo(this.canvas.width, 0);
                    this.context.lineTo(this.canvas.width / 2, 0);
                    this.context.lineTo(this.canvas.width / 2, this.canvas.height);
                    this.context.stroke();
                }
                this.$emit('confirm', null);
                this.context.restore();
            },

            /**
             *  保存图片 格式base64
             */
            saveAsImg() {
                if(this.config.isWrite == undefined){
                    return "";
                }
                const image = new Image();
                image.src = this.canvas.toDataURL(`image/${this.config.imgType}`);
                this.$emit('confirm',image.src);
                return image.src;
            },

            /**
             * 初始化画板
             */
            canvasInit () {
                this.canvas.width = this.config.canvasWidth * this.dpr;
                this.canvas.height = this.config.canvasHeight * this.dpr;
                this.canvas.style.width = `${this.config.canvasWidth}px`;
                this.canvas.style.height = `${this.config.canvasHeight}px`;
                this.config.emptyCanvas = this.canvas.toDataURL(`image/${this.config.imgType}`);
            },

            /**
             * 鼠标按下 => 下笔
             */
            handleMousedown(e){
                this.writeBegin({ x: e.offsetX || e.clientX, y: e.offsetY || e.clientY });
            },

            /**
             * 书写过程 => 下笔书写
             */
            handleMousemove(e){
                this.config.isWrite && this.writing({ x: e.offsetX, y: e.offsetY });
            },

            /**
             * 鼠标松开 => 提笔
             */
            handleMouseup(e){
                this.writeEnd({ x: e.offsetX, y: e.offsetY });
            },

            /**
             * 离开书写区域 => 提笔离开
             */
            handleMouseleave(e){
                this.config.isWrite = false;
                this.config.lastPoint = { x: e.offsetX, y: e.offsetY };
            },

            /* ==========================移动端兼容=Start================================ */

            /**
             * 手指按下 => 下笔
             */
            handleTouchstart(e){
                const touch = e.targetTouches[0];
                const x = touch.clientX ? touch.clientX - this.getRect().left :  touch.pageX - this.offset(touch.target,'left');
                const y = touch.clientY ? touch.clientY - this.getRect().top  : touch.pageY - this.offset(touch.target,'top');
                this.writeBegin({ x, y});
            },

            /**
             * 手指移动 => 下笔书写
             */
            handleTouchmove(e){
                const touch = e.targetTouches[0];
                const x = touch.clientX ? touch.clientX - this.getRect().left :  touch.pageX - this.offset(touch.target,'left');
                const y = touch.clientY ? touch.clientY - this.getRect().top  : touch.pageY - this.offset(touch.target,'top');
                this.config.isWrite && this.writing({ x, y });
            },

            /**
             * 手指移动结束 => 提笔离开
             */
            handleTouchend(e){
                const tcs = e.targetTouches;
                const ccs = e.changedTouches;
                const touch = tcs && tcs.length && tcs[0] || ccs && ccs.length && ccs[0];
                const x = touch.clientX ? touch.clientX - this.getRect().left :  touch.pageX - this.offset(touch.target,'left');
                const y = touch.clientY ? touch.clientY - this.getRect().top  : touch.pageY - this.offset(touch.target,'top');
                this.writeEnd({ x, y });
            },

            /* ==========================移动端兼容=End================================== */

            /**
             * 下载二维码到本地
             */
            downloadSignImg(name) {
                const c = document.getElementById(this.domId);
                const dataURL = c.toDataURL('image/png');
                this.saveFile(dataURL, name ? `${name}.${this.config.imgType}` : `${Date.parse(new Date())}.${this.config.imgType}`);
            },

            /**
             * 保存文件
             */
            saveFile(data, filename) {
                const saveLink = document.createElementNS('http://www.w3.org/1999/xhtml', 'a');
                saveLink.href = data;
                saveLink.download = filename;
                const event = document.createEvent('MouseEvents');
                event.initMouseEvent('click', true, false, window, 0, 0, 0, 0, 0, false, false, false, false, 0, null);
                saveLink.dispatchEvent(event);
            },

            /**
             * 获取画布的元素的大小及其相对于视口的位置
             * @return {}
             */
            getRect() {
                return this.$refs[this.domId].getBoundingClientRect();
            },

            /**
             * 获取dom对象的偏移量 可以获取解决position定位的问题
             * @returns number
             */
            offset(obj, direction) {
                //将top,left首字母大写,并拼接成offsetTop,offsetLeft
                const offsetDir = 'offset'+ direction[0].toUpperCase()+direction.substring(1);
                let realNum = obj[offsetDir];
                let positionParent = obj.offsetParent;  //获取上一级定位元素对象
                while(positionParent != null){
                    realNum += positionParent[offsetDir];
                    positionParent = positionParent.offsetParent;
                }
                return realNum;
            }
        }
    };
</script>



